During recent years there has been a trend in the cigarette industry towards lower yields of "tar" and nicotine. This has frequently been accomplished by increasing the filling power of the tobacco, namely, by putting less tobacco in the cigarette or by using more porous and/or faster burning cigarette papers. As a result of these measures the number of standard puffs obtainable from a cigarette has become reduced to the point that the cigarette burn rate is sometimes unacceptable to the consumer. It would be desirable, therefore, to reduce the cigarette burn rate while at the same time maintaining the above-mentioned benefits that were accrued before the burn rate was increased.
Various inorganic salts have been noted as promotors or as retardants of combustion in a variety of applications. Possible applicability to a cigarette is, however, subject to a number of restrictive requirements. Thus, any cigarette additive must be something which is easily applicable to tobacco and which exercises a significant effect at a low level consistent with its inclusion in a product such as a cigarette. Furthermore, neither the additive nor its decomposition products should be present in smoke in any amount inconsistent with commercial acceptability. Thus, the additive and its decomposition products should be present in smoke only at physiologically innocuous amounts. The additives should have relatively little effect on the yield of the various smoke components or, if there is any effect, it should be in a desirable direction. Of course, the additive should have a negligible adverse effect on taste. Another requirement is that any additive must be low in humectant properties so that at high relative humidities, e.g., above 60%, the treated tobacco does not absorb excessive amounts of moisture.
The burn rate of cigarettes is generally expressed quantitatively in one or more of three ways. One quantitative measurement consists in ascertaining the number of puffs obtainable from a given cigarette under the standard smoking regime wherein 2 second 35 cc puffs are taken once a minute to a butt length of 23 mm for non-filter cigarettes or tipping length plus 3 mm for filter cigarettes. Burn rate also may be quantitatively indicated by measuring the rate, expressed in mm/min, at which the tobacco column of the cigarette burns under free burning conditions. This measurement ordinarily is referred to as the linear burn rate. The third measurement, which is independent of tobacco packing density, is the mass burn rate. It is expressed in mg/min and calculated from the linear burn rate (LBR) and tobacco density according to the formula: ##EQU1## A tobacco is to be regarded as having a decreased burn rate, as this term is used herein and in the claims, if it exhibits decreased burn rate when measured by any one or more of these procedures.